This attack strategy guide is intended for players with SH (Stronghold) level 1-5.
At these stronghold levels, you'll be able to get access to the following troops:

Soldier (SH1)

Warden (SH1)

Mana Hunter (SH3)

Mauler (SH5)

In order to become a master attacker, you must plan your strategy several moves ahead, like a game of Chess. What troops should I use, where should I deploy them, where will they go next. What is my opponents weakness, and how can I exploit that weakness.
Let's take a look at all of these factors, starting with the available troops.

Troop Types

The Soldier - (melee) this troop is very tanky, it has high health, decent attack damage and 50% reduced physical damage. It cannot attack over walls, and is also weak against magic damage (Spell Towers). Being a melee troop with high health, it will often get the focus of the bulk of the defenses, which in turn allows your long ranged troops to freely do damage from behind. If they get hit by spell towers (splash damage), they may die early, which will leave your long ranged troops vulnerable to attack.

The Warden - (ranged) this troop is very fragile, it has low health, but decent damage. The biggest advantage is they can shoot over walls. Since they have low health, they are very vulnerable to splash damage towers such as Spell Towers and Catapults. It's often best to combine Wardens with Melee troops, however once Melee troops get inside the blind spot of a Catapult, it makes the wardens extremely vulnerable.

The Mana Hunter - (flying/ranged) these winged creatures are currently the only flying unit, so they have the advantage of avoiding defenses such as Catapults, which only attack ground units. They have medium health and very low damage, but on the plus side they will allow any troop to gain 1 extra Mana from every building destroyed nearby (a mana hunter icon will appear above nearby buildings). They are very vulnerable to Sky Watchers, which are the only anti-air defensive tower, which happens to deal splash damage too. Due to the mana hunters low damage, they aren't always that suitable for a 3 squad army, however they make an excellent support troop as a battle boost.

The Mauler - (melee) this troop makes a good tank, however they take up twice as much Portal Space as a Soldier. In comparison, a Mauler does less than half the damage of 2 soldiers, but around 20% more health. Maulers deal 3x the damage to walls and prioritize defenses, however they move slowly and are weak against crowd control. Watch out for spell towers equipped with Flash Freeze and Crippling Poison, as they will further slow their attack and movement speed. Due to their higher HP, they make a good distraction against Catapults.Note:Primus Conduits and Bunkers are both considered defensive buildings. Maulers may also attack through non-defensive buildings that are blocking their path.

Max level troops at SH5

Troop

Level

HP

Damage

slots

Prefer

Soldier

3

130

28.8

1

Any

Warden

3

50

28.5

1

Any

Mana Hunter

1

70

7.73

1

Any

Mauler

1

320

24 (72 vs walls)

2

Defense

Note: At SH level 5, your portals have a maximum of 5 troop slots which can only hold 2 Maulers, therefore it may be more beneficial to use a squad of 5 Soldiers instead.

There's 2 more crucial parts of your offensive line-up:

The Ancient - casting spells from your ancient is the key to keeping your troops alive as long as possible during battle. You're given Sulric to begin with, but you'll soon unlock plenty of other ancients such as Lyris, Foreveil, Kestra and Nyrax. Once you better understand these Ancients strengths, you'll be able to make a better choice based on the design of village you're up against.

The Dragon Roost - Once you've discovered your first Dragon (obtain Foreveil from the "Tracking Foreveil" Campaign on the map), you'll be able to build a Dragon Roost. You can assign a Dragon to your Dragon Roost, which will enable you to control it during battle, sweeping over the base, dealing damage and freezing defenses.

Cause damage or freeze targets by sweeping over them (possibly creating a deployment zone to drop troops in).

Use troops to clear defenses protecting the stronghold, allowing the dragon to freely take it down with it's ranged attack.

Defense Types

Now you know the strength and weaknesses of your available troops, it's time to find out what sort of defenses they'll be dealing with.

Watch Tower - Single Target - deals high damage to a single target, both ground and air troops. These towers are deadly against Dragons, but can easily be over-run by a squad of soldiers, maulers or Wardens.

Spell Tower (purple, Cursed Touch) - Splash Damage - deals low damage to a group of troops, increases damage taken by 10% and cannot be healed for 10 seconds. These towers will render Nyrax's Regeneration spell useless, however Sulric's Blackened Armour will dispel the towers debuff (which is the increased damage and anti-heal effect).Spell Tower (red, Flame Bolt) - Splash Damage - deals high damage to a group of troops, plus more high damage over 3 seconds. These towers can be easily over-run with a squad of troops, however it's best you first distract them with summons or your dragon.Spell Tower (yellow, Arc Lightning) - Splash Damage - deals very high damage to a group of troops in close proximity. Very deadly against Melee troops such as Soldiers and Maulers, but ranged troops such as Wardens can take it down without harm.Spell Tower (green, Crippling Poison) - Splash Damage - deals low damage to a group of troops, and reducing attack and movement speeds by 25%. This one is especially bad against Maulers, which already move and attack slowly.Spell Tower (blue, Flash Freeze) - Splash Damage - deals low damage to a group of troops, and freezes troops for 2.5 seconds. This spell will leave your troops vulnerable to any nearby defense. Distract them with the dragon, or summons.Spell Tower Notes: The level of the Spell Tower determines it's health and firing rate, and the level of the ancient attached determines the power of the spell.Spell Tower Tips:

The dragon can be useful for distracting spell towers such as Cursed Touch and Crippling Poison.

The dragon can attack an Arc Lightning Spell Tower without getting within range.

The dragon will not distract an Insanity Potion Spell Tower (you're unlikely to come across these at low level).

The dragon can be rendered useless against a Flash Freeze Spell Tower, since the dragon can be frozen.

The dragon might suffer a lot of damage against Flame Bolt Spell Towers, depending on the level of ancient attached to it.

Catapult - Splash Damage - slow firing, high damage to a group of ground targets. Has a blind spot up close. These can easily be taken down with melee troops, however that will draw their attention to long ranged troops such as wardens, so you might also want to use summons to distract them, or heal the troops with Nyrax's regeneration spell after they get hit. Nyrax's 15 mana 'Death' spell can potentially take it down in 1 shot.

Skywatcher - Splash Damage - slow firing, high damage to a group of air targets, including dragons. This can potentially kill a squad of Mana Hunters in 3-4 shots, so it's best to avoid deploying them anywhere near this tower. A dragon can potentially destroy a Skywatcher before it dies.

Primus Conduit - Increase Fire Speed - boosts the firing speed / recharge time of adjacent defenses (when charged). Watch out for anything connected to these conduits, as they could be damaging your troops 50% faster.

Bunker - Spawn Soldiers - not too dangerous, however they can stall and distract your troops, which can in turn take a lot of damage from defenses. They do not attack air troops.Note: when bunkers are attacking your troops, your troops won't retaliate until their current target is destroyed. This could be very dangerous when your troops are locked onto the stronghold (high HP).Note: Dragons will not trigger bunker troops, nor can the soldiers attack the dragon. Although Mana Hunters are a flying unit, they do trigger Bunker troops, and can be attacked by Soldiers.

Arrow Launcher - Splash Damage - very long range, ricochet damage to multiple troops. You might not come up against many of these at low SH level. Get into their blind spot to take them down, or use distractions to get their focus prior to dropping all your troops.

Troop Pathing

You now know what buildings each troop type prefers, but you also need to know how troops decide which building to target. It's fairly easy to determine which building they will initially target, since the building will be highlighted (not 100% accurate due to troop formation when deployed), but what will they target next?
There are many factors which determine the direction troops will travel. The distance, the number of walls blocking their way, and the total/remaining health of the walls.
Walls are a major factor when troops decide which direction to walk in. Most troops will target the closest building (or defense in case of Maulers), however if there's walls in the way, soldiers and paladins may decide to walk several tiles further (and much further if double layered) to reach an un-walled target (the higher the wall level, the bigger the factor). Maulers don't care as much about walls, if the closest defense is behind 1 layer of walls, they will attack through it! If there's 2 layers of walls, Maulers may choose a slightly longer path. Ranged troops such as wardens will attack over walls to reach a target within range, so they may tend to walk outside walls to reach their next target too.
Mana Hunters and Dragons totally ignore walls, they always target the closest building.
If there are Bunker Troops in the area, they also become a factor (treated similar to targeting a building).Note: your troops won't attack bunker troops until they've destroyed the target they are currently attacking.
If you don't consider troop pathing before starting an attack, then you may find some of your troops wondering off in unexpected directions, potentially causing an early loss.

So what can we do to ensure troops go where we want them to? Well, 1 way would be to find a point of entry where there's a lack of distractions outside the walls, this will often cause troops to attack straight through the walls to reach the stronghold.
Another alternative is to clear outside buildings using the Dragon from the Roost. Since you can control the dragon, you can sweep it from 1 location to another, and clear distractions either side of your chosen point of entry. Be mindful of the time limit though, as the dragon does low damage.
For bases with multiple layers of walls, it is often useful to use a squad of Maulers so they will attack through the wall(s) to the nearest defense, this will help with soldier/paladin pathing.

Ancients

At SH level 5, you do have access to a lot of Rare & Epic Ancients in Loyalty chests, Relic chests and Ancient chests, however the chance of getting the common and superior ancients is far greater than getting the more powerful Rare & Epic ancients. Therefore i'll focus on the former for the purpose of this guide.
Please refer to the ancients table for a list of Common (grey) and Superior (green) ancients.

When you unlock each one, do a few attacks to get familiar with their abilities.

At stronghold levels 1-5, you only have 3 Troop Portals, so you must choose your squads wisely.
As mentioned earlier, ranged troops are fragile, so it's important to pair them up with melee troops. You need the right amount of melee troops so they'll survive long enough to keep the focus away from your ranged troops.
It's a good idea to go with 2 squads of Melee + 1 squad of Ranged.
Depending on the base design you're attacking, you may decide to go with more ranged troops instead of melee, or possibly all melee troops.
So how do you know which troops and ancient to use in battle? Well that totally depends on the base you come up against.
Every base has a weakness, it's just a matter of finding out what that weakness is, then choosing the appropriate troops and ancient to deal with that weakness.
Let's take a look at a few examples.

Attack Strategy Examples

Example 1 - Nyrax

Against this layout, I decided to go with Nyrax and a full Warden army.
Fortunately, 1 of the catapults was upgrading, so that could be completely ignored. If it was active, then 1 Warden could have been substituted for 1 soldier/Mauler, and deployed at the Watch Tower to distract the Catapult. This would give Wardens time to finish off the troops portals and take it down before the Soldiers die off.
The bulk of the mana is in one spot, the Troop Portals. The Wardens and the Dragon can reach this without taking damage.
Once this is cleared, the next issue is the Catapult behind the Stronghold. Since I already gained more than 15 mana from the Troop Portals, the Catapult can be taken down in 1 shot with Nyrax's 3rd Spell, Death.
The Arc Lightning Spell Tower on the left isn't an issue, since Wardens can reach it without getting within range. That just leaves the Flame Bolt Spell Tower in the east. Once the troops finish off the Stronghold, you can once again use the "Death" spell to destroy the Spell Tower.
At any time, Foreveil can be used to freeze defenses, help take down or distract defenses, or snipe the Stronghold.

Example 2 - Foreveil

In this layout, the Stronghold is fairly well protected with defenses. Since it's using Flash Freeze Spell Tower, I decided to go with Foreveil, and a full Soldier Army.
Not only does Foreveil's first spell "Frost Shield" give immunity to freeze, but it also gives 35% reduced damage. On top of that, Soldiers also have 50% reduced physical damage, which will really help against all the other defenses.
I used Foreveil to destroy the 2 outside Gold Storage and Troop Portal, then swept the dragon over to the Barracks in the west. Taking this building down will help the Soldiers path into the Spell Tower and Watch Tower.
Next, I swept Foreveil across the entire base to the Blacksmith in the east, this triggers the Flash Freeze Spell Tower.
I deployed all the Soldiers at the Troop Portals in the south, and deployed Foreveil's "Frost Shield" spell just before the Flash Freeze Spell Tower fires.
Once the Soldiers get within range of the Catapult, you can use Foreveil to sweep over it to freeze it, as well as deploy "Frost Shield" on the Soldiers.
Once the Stronghold falls, I used "Midwinter" to freeze all the remaining defenses.Note: There is an open troop deployment zone next to the Catapult. For the purpose of this guide I ignored it, however I could have easily deployed 1 squad of troops there to take down the Catapult.

Example 3 - Lyris

This layout has a lot of scattered buildings, and a lot of walled defenses surrounding the Stronghold. This is the reason why I went with 3 Wardens.
Although there's many suitable ancients against this layout, I chose Lyris because of her 1st spell, "Lightning Bolt". It does extra damage on the first strike on each building, so this is a good way to assist your troops in taking down each defense. With the large amount of free mana outside, I was able to cast this spell many times.
I deployed Foreveil at the outside Troop Portals, sweeping to other portals once she had built up a recharge. When I had enough mana, I used "Lightning Bolt" on the southern Catapult and surrounding Watch Towers. When time was running low, I swept Foreveil within range of the Flash Freeze Spell Tower to distract it, then deployed a squad of Wardens to take down the Catapult and Spell Tower.
The other 2 squads of Wardens were used to take down Watch Towers, which were then in free range of the Stronghold. "Lightning Bolt" was used to help take down any left-over defenses, and Foreveil used to help snipe the Stronghold.

Example 4 - Sulric

This layout has a lot of defenses close the the Stronghold. Here I chose to use Sulric and mostly Maulers. The Maulers will help aim straight for the defenses, and Sulric's 1st Spell, "Rain of Fire" will help damage a clump of buildings.
At first I deployed Foreveil to take down a Troop Portal. This gave me enough mana to drop "Rain of Fire" on the Catapult, which also took down the Builder's Huts. This opened up a troop deployment zone, allowing me to drop a squad of Maulers to help take down the Catapult.
Another squad of Maulers were also deployed where the Troop Portal was.
Each time 5 mana was gained, Sulric's "Rain of Fire" was deployed on a clump of defenses.
Once the Spell Tower and Catapult was taken down, the Wardens were deployed to help take the Stronghold down.

Example 5 - Eloni

This layout has a Catapult and Flame Bolt Spell Tower which is difficult to get to. To deal with the Spell Tower, I chose Eloni.
Eloni's 1st Spell "Fire Frenzy" renders troops completely immune to Flame Bolt Spell Towers, but first I had to gain enough mana to cast it.
I dropped Foreveil in the south to take down the Troop Portal.
Just as that was finishing, I dropped a squad of Maulers at the Watch Tower to distract the Catapult.
Once the Troop Portal was destroyed, I swept the Dragon over the Spell Tower to trigger it off.
This gave me some time to deploy the squad of Soldiers and Wardens, and cast the "Fire Frenzy" spell before it hit my troops.
The Spell Tower went down will minimal damage, followed by the Catapult, which was still distracted by the Maulers.